JP5616283B2 - Fe-Ni-Cr-Mo alloy and method for producing the same - Google Patents

Fe-Ni-Cr-Mo alloy and method for producing the same Download PDF

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JP5616283B2
JP5616283B2 JP2011097224A JP2011097224A JP5616283B2 JP 5616283 B2 JP5616283 B2 JP 5616283B2 JP 2011097224 A JP2011097224 A JP 2011097224A JP 2011097224 A JP2011097224 A JP 2011097224A JP 5616283 B2 JP5616283 B2 JP 5616283B2
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篤 藤田
篤 藤田
和貴 西嶋
和貴 西嶋
雄一 神戸
雄一 神戸
室恒 矢部
室恒 矢部
轟 秀和
秀和 轟
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Nippon Yakin Kogyo Co Ltd
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Description

本発明は、耐衝撃性及び表面性状に優れ、かつニッケル製錬プラントや海洋構造物等への使用に耐えるFe−Ni−Cr−Mo合金およびその製造方法に関するものである。   The present invention relates to an Fe—Ni—Cr—Mo alloy excellent in impact resistance and surface properties and resistant to use in nickel smelting plants, offshore structures, and the like, and a method for producing the same.

例えばオーステナイト系ステンレス鋼などのようなクロム及びモリブデン含有合金は、その良好な耐食性から様々な分野で利用されている。しかしながら、ニッケル製錬プラントや海洋構造物などに用いる場合には、全面腐食や孔食等極めて有害な腐食が生じ易く、汎用オーステナイト系ステンレス鋼であるSUS304やSUS316等では耐食性は充分ではなかった。そこで、耐食性の向上を図るため、CrやMoの含有量を増加し、Nを添加する試みがなされてきた。例えば特許文献1には、オーステナイト系ステンレス鋼の耐食性は一般に下記(1)式で表される数値で評価でき、この数値が高いほど優れた耐食性を示すことが開示されている。   For example, chromium and molybdenum-containing alloys such as austenitic stainless steel are used in various fields because of their good corrosion resistance. However, when used in nickel smelting plants, offshore structures, etc., extremely harmful corrosion such as full surface corrosion and pitting corrosion is likely to occur, and general-purpose austenitic stainless steels such as SUS304 and SUS316 have not been sufficiently resistant to corrosion. Therefore, attempts have been made to increase the content of Cr and Mo and add N in order to improve the corrosion resistance. For example, Patent Document 1 discloses that the corrosion resistance of austenitic stainless steel can be generally evaluated by a numerical value represented by the following formula (1), and the higher this numerical value, the better the corrosion resistance is disclosed.

[数1]
Cr+3.3×Mo+16×N (1)
(Cr、Mo、Nは各成分元素の含有量(質量%))
[Equation 1]
Cr + 3.3 × Mo + 16 × N (1)
(Cr, Mo, N is the content of each component element (mass%))

特開2010−31313号公報JP 2010-31313 A

オーステナイト系ステンレス鋼において耐食性を向上させるためには、上記(1)式から分かるように、Cr、Mo、Nの含有量を高める必要がある。しかしながら、Cr、Mo、Nの含有量が増加すると、σ相やχ相の金属間化合物やCr−Mo系窒化物が析出し易くなって耐衝撃性が低下し、板材の製造ができなくなることがあった。すなわち、熱間圧延にてコイルを製造した後の冷却時にσ相等が析出し、次工程においてコイルを巻き戻す際にσ相等を起点として破断に至ることがあった。さらに、板材に析出した非金属介在物が表面に存在すると表面疵となり、製品としての商品価値を損なうばかりでなく、耐食性等への品質特性にも悪影響を及ぼす。   In order to improve the corrosion resistance in the austenitic stainless steel, it is necessary to increase the contents of Cr, Mo and N as can be seen from the above equation (1). However, if the content of Cr, Mo, N increases, intermetallic compounds of σ phase and χ phase and Cr-Mo nitrides are likely to be precipitated, impact resistance is lowered, and it becomes impossible to produce a plate material. was there. That is, a σ phase or the like may precipitate during cooling after the coil is manufactured by hot rolling, and may break when the coil is rewound in the next process. Furthermore, if non-metallic inclusions deposited on the plate material are present on the surface, they become surface defects, which not only impair the commercial value of the product but also adversely affect the quality characteristics such as corrosion resistance.

また、CrやMoは高価な金属であるため、その含有量を高めると製造コストが増加する。さらに、Nは、安価に入手できる合金元素であり、オーステナイト相安定化元素であるため、金属間化合物の析出を抑える効果があるが、大気圧下で溶解する場合には、溶存可能なN濃度には限度がある。このため、大気圧下でのNの平衡濃度を超えて溶解させるためには、加圧溶解炉などの特殊な設備が必要となる。一方、鋼中のN濃度が高まるにつれて鋼の強度も高まるため、加工が困難となる。   Further, since Cr and Mo are expensive metals, increasing their content increases the manufacturing cost. Furthermore, N is an alloy element that can be obtained at a low cost, and since it is an austenite phase stabilizing element, it has an effect of suppressing the precipitation of intermetallic compounds. However, when dissolved under atmospheric pressure, the dissolved N concentration Has a limit. For this reason, in order to make it melt | dissolve exceeding the equilibrium concentration of N under atmospheric pressure, special facilities, such as a pressure melting furnace, are needed. On the other hand, as the N concentration in the steel increases, the strength of the steel also increases, which makes processing difficult.

本発明は、上記従来技術の問題点を解決するためになされたものであり、耐衝撃性及び表面性状に優れ、ニッケル製錬プラント及び海洋構造物等への使用に耐えるFe−Ni−Cr−Mo合金およびその製造方法を提供することを目的としている。   The present invention has been made in order to solve the above-mentioned problems of the prior art, and is excellent in impact resistance and surface properties, and can be used for nickel smelting plants and offshore structures. It aims at providing Mo alloy and its manufacturing method.

発明者らは、まず、種々の鋼材に対してシャルピー衝撃試験により耐衝撃性を測定した。衝撃値が低いとσ相がより多く析出し、脆化を起こしていることを示す。鋼材の成分については、成分規格範囲内(ASTM B625−05 UNS N08031)においてSi、Mn含有量が高く、σ相やχ相などの金属間化合物の析出を抑制する上で有効な元素であるNiおよびN濃度を高めに成分設計した鋼塊を作製したところ、耐衝撃性が悪く、板材の製造は不可能と判断された。この原因を探るべく、試験片のミクロ組織観察を行ったところ、粒界および粒内に多くのσ相が析出し、脆化していたことが判った。そこでσ相生成を助長させる元素であるSi、Mnの含有量を少なくした鋼塊を作製し、シャルピー衝撃試験を行った結果、高い衝撃値が得ることができた。その試料においてもミクロ組織観察を行ったところ、σ相が著しく減少していることが判った。以上の知見からSi:0.30質量%以下、Mn:0.50質量%以下であるとσ相が析出せず、耐衝撃性が向上し、脆化しないことを見出した。   The inventors first measured impact resistance of various steel materials by Charpy impact test. If the impact value is low, more σ phase is precipitated, indicating that embrittlement has occurred. As for the components of steel materials, Ni is an element effective in suppressing precipitation of intermetallic compounds such as σ phase and χ phase with high Si and Mn contents within the component specification range (ASTM B625-05 UNS N08031). Further, when a steel ingot having a component design with a high N concentration was produced, the impact resistance was poor and it was judged that production of a plate material was impossible. In order to investigate the cause, the microstructure of the test piece was observed. As a result, it was found that many σ phases were precipitated at the grain boundaries and in the grains and were embrittled. Therefore, as a result of producing a steel ingot with a reduced content of Si and Mn, which are elements for promoting the generation of σ phase, and conducting a Charpy impact test, a high impact value was obtained. When the microstructure was also observed in the sample, it was found that the σ phase was significantly reduced. From the above knowledge, it was found that when Si: 0.30 mass% or less and Mn: 0.50 mass% or less, the σ phase does not precipitate, impact resistance is improved, and embrittlement does not occur.

本発明のFe−Ni−Cr−Mo合金は、上記知見に基づいてなされたもので、質量%で、C:0.001〜0.015%、Si:0.01〜0.30%、Mn:0.01〜0.50%、P:0.020%以下、S:0.0015%以下、Ni:30.00〜32.00%、Cr:26.00%を超え28.00%以下、Mo:6.00〜7.00%、Cu:1.00%を超え1.40%以下、Al:0.001〜0.10%、N:0.15〜0.25%、B:0.0005〜0.0030%、Ca:0.0001〜0.0020%、Mg:0.0001〜0.0050%、O:0.0001〜0.0050%、残部:Feおよび不可避不純物からなることを特徴としている。   The Fe—Ni—Cr—Mo alloy of the present invention was made based on the above knowledge, and in mass%, C: 0.001 to 0.015%, Si: 0.01 to 0.30%, Mn : 0.01 to 0.50%, P: 0.020% or less, S: 0.0015% or less, Ni: 30.00 to 32.00%, Cr: more than 26.00% and 28.00% or less , Mo: 6.00 to 7.00%, Cu: more than 1.00% and 1.40% or less, Al: 0.001 to 0.10%, N: 0.15 to 0.25%, B: 0.0005 to 0.0030%, Ca: 0.0001 to 0.0020%, Mg: 0.0001 to 0.0050%, O: 0.0001 to 0.0050%, balance: Fe and inevitable impurities It is characterized by that.

また、上記の鋼塊から作製した板材における表面疵の詳細な調査・研究を行った結果、表面疵の原因は、クラスター状のMgO・Alスピネル、あるいは大型化した非金属介在物であることが判った。特に、MgO・Alスピネルは高融点かつ硬質であり、加えてクラスター化しやすいことから、表面疵の原因となり易い。このような調査結果をもとに非金属介在物の組成、サイズに関して検討を行い、非金属介在物の組成がMgO、MgO・Alスピネル、CaO−Al−MgO系酸化物のいずれか1種または2種以上からなり、かつ長径3μm以上からなる非金属介在物のうち、長径が50μm以上となる非金属介在物の個数比率が20%以下であれば、表面疵が発生しないことが判った。また、合金中酸素濃度が50ppmを超えると非金属介在物の量が多くなるのと同時に大型になることで、表面疵が発生することも分かった。 In addition, as a result of detailed investigation and research on surface flaws in the plate material made from the above steel ingot, the cause of surface flaws is cluster-like MgO / Al 2 O 3 spinel or large non-metallic inclusions. It turns out that there is. In particular, MgO.Al 2 O 3 spinel has a high melting point and is hard, and in addition, is easily clustered, and thus easily causes surface defects. Based on such investigation results, the composition and size of non-metallic inclusions are examined, and the composition of non-metallic inclusions is MgO, MgO.Al 2 O 3 spinel, CaO—Al 2 O 3 —MgO-based oxide. If the number ratio of nonmetallic inclusions having a major axis of 50 μm or more is 20% or less among nonmetallic inclusions comprising one or more of these and having a major axis of 3 μm or more, surface flaws are generated. It turns out not to. It has also been found that when the oxygen concentration in the alloy exceeds 50 ppm, the amount of non-metallic inclusions increases, and at the same time, the surface becomes flawed due to an increase in size.

したがって、本発明は、非金属介在物としてMgO、MgO・Alスピネル、CaO−Al−MgO系酸化物のいずれか1種または2種以上を含み、長径が3μm以上の非金属介在物のうち、MgO・Alスピネルの個数比率が50%以下で、長径が30μm以上の非金属介在物の個数比率が20%以下であることを好ましい態様としている。 Therefore, the present invention includes one or more of MgO, MgO.Al 2 O 3 spinel, and CaO—Al 2 O 3 —MgO-based oxide as non-metallic inclusions, and the major axis has a length of 3 μm or more. Of the metal inclusions, the number ratio of MgO.Al 2 O 3 spinel is 50% or less, and the number ratio of nonmetallic inclusions having a major axis of 30 μm or more is 20% or less.

また、本発明は、上記Fe−Ni−Cr−Mo合金の製造方法であり、電気炉に原料を装入し、質量%で、Cr:26.00%を超え28.00%以下、Ni:30.00〜32.00%、Mo:6.00〜7.00%含有するFe−Cr−Ni−Mo合金溶湯を溶製し、次いで、AOD精錬、VOD精錬、およびAOD精錬に続きVOD精錬の3通りのいずれかの処理で脱炭した後に、石灰、蛍石、フェロシリコン合金およびAlを投入し、CaO/Al比:3〜10、CaO/SiO比:5〜20、MgO:3〜10質量%からなるCaO−SiO−MgO−Al−F系スラグを用い、上記Fe−Ni−Cr−Mo合金の成分組成となるように溶鋼成分の調整を行い、その後、該合金溶湯を連続鋳造法、または普通造塊法にて鋳造し、スラブを製造することを特徴とする。 The present invention is also a method for producing the above-described Fe—Ni—Cr—Mo alloy, in which a raw material is charged into an electric furnace, and in mass%, Cr: more than 26.00% and not more than 28.00%, Ni: A Fe—Cr—Ni—Mo alloy melt containing 30.00 to 32.00% and Mo: 6.00 to 7.00% is melted, and then VOD refining following AOD refining, VOD refining, and AOD refining After decarburizing by any one of the three treatments, lime, fluorite, ferrosilicon alloy and Al are added, CaO / Al 2 O 3 ratio: 3-10, CaO / SiO 2 ratio: 5-20, MgO: Using CaO—SiO 2 —MgO—Al 2 O 3 —F-based slag composed of 3 to 10% by mass, adjusting the molten steel components so as to be the component composition of the Fe—Ni—Cr—Mo alloy, Thereafter, the molten alloy is continuously cast or It is characterized by casting a slab by a conventional ingot method.

本発明によれば、ニッケル製錬プラントや海洋構造物等に使用されるFe−Ni−Cr−Mo合金の耐衝撃性を著しく改善することが可能であり、コイルによる板材の生産が可能になるとともに、非金属介在物起因の表面疵を大幅に低減することができるので、生産性の向上と製品歩留の向上のみならず品質向上にも寄与する。   According to the present invention, it is possible to remarkably improve the impact resistance of an Fe—Ni—Cr—Mo alloy used in a nickel smelting plant, an offshore structure or the like, and it is possible to produce a plate material using a coil. At the same time, surface flaws caused by non-metallic inclusions can be greatly reduced, which contributes not only to improved productivity and product yield, but also to improved quality.

まず、本発明に用いる鋼の化学成分の限定理由について説明する。なお、以下の説明において「%」は「質量%」を意味する。   First, the reasons for limiting the chemical components of the steel used in the present invention will be described. In the following description, “%” means “mass%”.

C:0.001〜0.015%
Cは、合金に強度を付与するために必要な元素であるため0.001%以上含有させる必要がある。しかしながら、0.015%を超えて含有すると、溶接熱影響部あるいは固溶化熱処理後の冷却速度が遅い場合において、結晶粒界に(Cr、Fe)23として析出し、Cr欠乏層を生成することにより、本合金の耐粒界腐食性を劣化させる。したがって、Cの上限を0.015%とした。
C: 0.001 to 0.015%
Since C is an element necessary for imparting strength to the alloy, it is necessary to contain 0.001% or more. However, when the content exceeds 0.015%, when the cooling rate after the heat affected zone or the solution heat treatment is slow, (Cr, Fe) 23 C 6 precipitates at the grain boundary to form a Cr-depleted layer. By doing so, the intergranular corrosion resistance of this alloy is deteriorated. Therefore, the upper limit of C is set to 0.015%.

Si:0.01〜0.30%
Siは、脱酸のために有効な元素であって0.01%以上の添加が必要である。しかしながら、過剰に添加してもその効果が飽和するとともに、延性の低下や強度の上昇を招き、さらに耐衝撃性を低下させるσ相やχ相などの金属間化合物の析出を抑制し、また耐食性劣化を抑制するには過剰な添加は抑える必要があるため、Siの上限を0.30%とした。
Si: 0.01-0.30%
Si is an effective element for deoxidation and needs to be added in an amount of 0.01% or more. However, even if added excessively, the effect is saturated, the ductility is lowered and the strength is increased, and the precipitation of intermetallic compounds such as σ phase and χ phase, which lowers the impact resistance, is suppressed, and the corrosion resistance. Since it is necessary to suppress excessive addition to suppress the deterioration, the upper limit of Si is set to 0.30%.

Mn:0.01〜0.50%
Mnは、脱酸のために有効な元素であって0.01%以上の添加が必要である。しかしながら、耐衝撃性を低下させるσ相やχ相などの金属間化合物の析出を抑制し、また耐食性劣化を抑制するには過剰な添加は抑える必要があるため、Mnの上限を0.50%とした。
Mn: 0.01 to 0.50%
Mn is an effective element for deoxidation and needs to be added in an amount of 0.01% or more. However, since it is necessary to suppress excessive addition in order to suppress precipitation of intermetallic compounds such as σ phase and χ phase that reduce impact resistance and to suppress deterioration of corrosion resistance, the upper limit of Mn is 0.50%. It was.

P:0.020%以下
Pは、不純物として不可避的に混入する元素であり、結晶粒界に偏析し易く、耐食性および熱間加工性の観点からは少ない方が望ましいので、含有量は0.020%以下とする。
P: 0.020% or less P is an element that is inevitably mixed in as an impurity, is easily segregated at the grain boundary, and is preferably smaller in terms of corrosion resistance and hot workability. 020% or less.

S:0.0015%以下
Sは、Pと同様に不可避的に混入する元素であり、結晶粒界に偏析、または硫化物を形成し、孔食等の耐食性および熱間加工性を劣化させる元素であることから、その含有量は0.0015%以下とする。
S: 0.0015% or less S is an element that is inevitably mixed in the same manner as P, and is an element that segregates or forms sulfides at grain boundaries and deteriorates corrosion resistance such as pitting corrosion and hot workability. Therefore, the content is made 0.0015% or less.

Ni:30.00〜32.00%
Niは、オーステナイト相生成元素であり、σ相やχ相などの金属間化合物の析出を抑制する上で有効な元素であって30.00%以上の添加が必要である。ただし、Niは溶鋼中のNの溶解度を低下させる性質も併せ持つことから、その含有量は32.00%以下とする。
Ni: 30.00 to 32.00%
Ni is an austenite phase generating element, and is an effective element for suppressing precipitation of intermetallic compounds such as σ phase and χ phase, and needs to be added in an amount of 30.00% or more. However, since Ni also has the property of reducing the solubility of N in molten steel, its content is set to 32.00% or less.

Cr:26.00%を超え28.00%以下
Crは、耐食性を向上させる元素であるため26.00%を超えて含有する。しかしながら、Crはσ相やχ相等の金属間化合物の形成を助長し、かえって耐食性を劣化させるため、28.00%以下とする。
Cr: more than 26.00% and not more than 28.00% Since Cr is an element that improves corrosion resistance, it contains more than 26.00%. However, Cr promotes the formation of intermetallic compounds such as σ phase and χ phase, and rather deteriorates the corrosion resistance.

Mo:6.00〜7.00%
Moは、耐食性を向上させるために有効な元素であるが、7.00%を超えて含有すると、Crと同様にσ相やχ相などの金属間化合物の生成を助長し、耐食性をかえって劣化させるので、6.00〜7.00%以下とした。
Mo: 6.00 to 7.00%
Mo is an effective element for improving the corrosion resistance. However, when it is contained in an amount exceeding 7.00%, it promotes the formation of intermetallic compounds such as σ phase and χ phase like Cr and deteriorates by changing the corrosion resistance. Therefore, the content is made 6.00 to 7.00% or less.

Cu:1.00%を超え1.40%
Cuは、耐酸性を向上させるために有効な元素であり、その効果を得るためには1.00%を超えて含有する必要がある。しかしながら、1.40%を超えて含有すると、熱間加工性を低下させるため1.00〜1.40%とした。
Cu: more than 1.00% and 1.40%
Cu is an effective element for improving acid resistance, and in order to obtain the effect, it is necessary to contain more than 1.00%. However, if the content exceeds 1.40%, the hot workability is lowered, so the content was made 1.00 to 1.40%.

Al:0.001〜0.10%
Alは、有効な脱酸元素であるが、0.001%以上含有しないとその効果が得られない。一方、Alの含有量が0.10%を超えると、脱酸の効果が飽和する。また、Alは金属間化合物の析出を助長し、スラグ中のCaOを還元により溶鋼中のCa濃度上昇を招き、CaO含有介在物の生成を促して耐食性の劣化を招く。そこで、上限を0.10%と定めた。
Al: 0.001 to 0.10%
Al is an effective deoxidizing element, but its effect cannot be obtained unless it contains 0.001% or more. On the other hand, when the Al content exceeds 0.10%, the effect of deoxidation is saturated. In addition, Al promotes precipitation of intermetallic compounds, causes Ca concentration increase in molten steel by reducing CaO in slag, promotes formation of inclusions containing CaO, and deteriorates corrosion resistance. Therefore, the upper limit is set to 0.10%.

N:0.15〜0.25%
Nは、強力なオーステナイト相生成元素であるとともに、CrやMoと同様に耐食性を向上させるために有効な元素である。また、Nは、金属間化合物の析出を抑制するのに有効であり、その効果を得るためには0.15%以上含有する必要がある。しかしながら、鋼中にNを多量に含有させると熱間変形抵抗が高くなり、熱間圧延が困難になるため、0.15〜0.25%とした。
N: 0.15-0.25%
N is a strong austenite phase forming element and an element effective for improving the corrosion resistance like Cr and Mo. N is effective in suppressing the precipitation of intermetallic compounds, and in order to obtain the effect, it is necessary to contain 0.15% or more. However, when a large amount of N is contained in the steel, the hot deformation resistance becomes high and hot rolling becomes difficult, so the content was made 0.15 to 0.25%.

B:0.0005〜0.0030%
Bは、熱間加工性の向上に対して、極めて有効な元素であるが、その含有量が0.0005%に満たないとその効果は小さい。一方、過剰な添加はかえって熱間加工性を阻害する。そこで、上限を0.0030%とした。
B: 0.0005 to 0.0030%
B is an extremely effective element for improving hot workability, but its effect is small if its content is less than 0.0005%. On the other hand, excessive addition inhibits hot workability. Therefore, the upper limit was made 0.0030%.

O:0.0001〜0.0050%
Oは、Al、Mg、Caなどと反応し、非金属介在物を生成する。Oの濃度が0.0050%を超えると、非金属介在物の量が多くなるのと同時に大型になることで、表面疵が発生することから、その上限を0.0050%とした。また、合金に含まれる非金属介在物の個数は少ない方が好ましいが、極端に低減するには製造コストの上昇をもたらす。そこで、下限は0.0001%とした。
O: 0.0001 to 0.0050%
O reacts with Al, Mg, Ca and the like to generate non-metallic inclusions. If the concentration of O exceeds 0.0050%, the amount of non-metallic inclusions increases and at the same time, the surface becomes flawed, so the upper limit was made 0.0050%. Moreover, although it is preferable that the number of non-metallic inclusions contained in the alloy is small, an extremely low reduction leads to an increase in manufacturing cost. Therefore, the lower limit was made 0.0001%.

Ca:0.0001〜0.0020%
Caは、非金属介在物をCaO−Al−MgO系酸化物に制御するために有用な元素であり、精錬工程において、スラグや耐火物中のCaOが還元されることによって溶鋼中に供給される。しかしながら、Caの含有量が0.0020%を越えると、非金属介在物中のCaO濃度を上昇させ、耐食性に悪影響を与えることに加えて、30μmを超えるサイズのCaO−Al−MgO系酸化物が発生し、製品板の表面欠陥を発生させることから、その濃度には限界がある。そこで、本発明では、Caの含有量を、0.0001〜0.0020%とした。
Ca: 0.0001 to 0.0020%
Ca is an element useful for controlling non-metallic inclusions to CaO—Al 2 O 3 —MgO-based oxides. In the refining process, CaO in the slag and refractory is reduced in the molten steel. Supplied. However, if the Ca content exceeds 0.0020%, the CaO concentration in the non-metallic inclusions is increased, adversely affecting the corrosion resistance, and in addition to CaO—Al 2 O 3 —MgO having a size exceeding 30 μm. Since the system oxide is generated and surface defects of the product plate are generated, the concentration is limited. Therefore, in the present invention, the Ca content is set to 0.0001 to 0.0020%.

Mg:0.0001〜0.0050%
Mgは、熱間加工性向上に有効な元素であると共に、非金属介在物組成をMgO、MgO・AlスピネルまたはCaO−Al−MgO系酸化物のうちの1種または2種以上に制御するために必要な元素であり、精錬工程において、スラグや耐火物中のMgOが還元されることによって溶鋼中に供給される。しかしながら、Mgの含有量が0.0050%を超えると、非金属介在物として硬質なMgO・Al系が主体となり、表面疵を引き起こす大型非金属介在物の存在頻度が増すため、Mgの含有量には限界がある。そこで本発明では、Mgの含有量を、0.0001〜0.0050%とした。
Mg: 0.0001 to 0.0050%
Mg is an element effective for improving hot workability, and the nonmetallic inclusion composition is one or two of MgO, MgO.Al 2 O 3 spinel, or CaO—Al 2 O 3 —MgO-based oxide. It is an element necessary to control more than the seed, and is supplied into the molten steel by reducing MgO in the slag and the refractory in the refining process. However, if the Mg content exceeds 0.0050%, the hard non-metallic inclusions are mainly composed of hard MgO.Al 2 O 3 and the presence frequency of large non-metallic inclusions that cause surface flaws increases. The content of is limited. Therefore, in the present invention, the Mg content is set to 0.0001 to 0.0050%.

非金属介在物
本発明では、Fe−Ni−Cr−Mo合金に含有される非金属介在物は、MgO、MgO・Alスピネル、CaO−Al−MgO系酸化物のいずれか1種または2種以上を含み、長径が3μm以上の非金属介在物のうち、MgO・Alスピネルの個数比率が50%以下で、長径が30μm以上の非金属介在物の個数比率が20%以下であることを好ましい態様としている。以下、非金属介在物の組成、並びに個数比率限定の根拠を示す。
Non-metallic inclusions In the present invention, the non-metallic inclusions contained in the Fe-Ni-Cr-Mo alloy are any of MgO, MgO.Al 2 O 3 spinel, and CaO-Al 2 O 3 -MgO-based oxides. Among non-metallic inclusions containing one or more types and having a major axis of 3 μm or more, the number ratio of MgO · Al 2 O 3 spinel is 50% or less and the number ratio of non-metallic inclusions having a major axis of 30 μm or more is The preferred embodiment is 20% or less. Hereinafter, the composition of nonmetallic inclusions and the basis for limiting the number ratio will be shown.

MgO、MgO・Al 、CaO−Al −MgO系酸化物のうちの1種または2種以上を含み、長径が3μm以上の非金属介在物のうち、MgO・Al スピネルの個数比率が50%以下
これらの酸化物系非金属介在物は、フェロシリコンとAlにより脱酸した際に生成される脱酸生成物である。本発明に係るFe−Ni−Cr−Mo合金は、合金中のAl、Mg、Caの含有量に従い、MgO、MgO・Alスピネル、CaO−Al−MgO系酸化物のうちの1種または2種以上を含む。しかしながら、MgO・Alスピネルの個数比率が50%を超えて存在した場合、MgO・Alスピネルからなるクラスターを形成しやすくなり、大型非金属介在物の個数比率が多くなり、表面疵を発生させる。したがって、大型非金属介在物の個数比率を制限するためには、MgO・Alスピネルの個数比率を50%以下とすることが望ましい。
Among non-metallic inclusions containing one or more of MgO, MgO.Al 2 O 3 , CaO—Al 2 O 3 —MgO-based oxide and having a major axis of 3 μm or more, MgO.Al 2 O 3 The number ratio of spinel is 50% or less. These oxide-based nonmetallic inclusions are deoxidation products generated when deoxidation is performed with ferrosilicon and Al. The Fe—Ni—Cr—Mo alloy according to the present invention includes MgO, MgO · Al 2 O 3 spinel, and CaO—Al 2 O 3 —MgO-based oxides according to the contents of Al, Mg, and Ca in the alloy. 1 type or 2 types or more are included. However, when the number ratio of MgO · Al 2 O 3 spinel exceeds 50%, it becomes easier to form a cluster composed of MgO · Al 2 O 3 spinel, and the number ratio of large non-metallic inclusions increases. Generates surface flaws. Therefore, in order to limit the number ratio of large non-metallic inclusions, the number ratio of MgO.Al 2 O 3 spinel is desirably 50% or less.

長径が30μm以上となる非金属介在物の個数比率が20%以下
MgO・Alスピネルから形成されるクラスターや、脱酸が不十分の際に合金中に生成される大型非金属介在物が表面疵を発生させる起因となる。しかしながら、長径3μm以上からなる非金属介在物のうち、長径が30μm以上となる非金属介在物の個数比率が20%以下であれば、表面欠陥が発生しないことが判った。よって、長径3μm以上からなる非金属介在物のうち、長径が30μm以上となる非金属介在物の個数比率は20%以下であることが望ましい。
The number ratio of non-metallic inclusions having a major axis of 30 μm or more is 20% or less. Clusters formed from MgO · Al 2 O 3 spinel and large non-metallic inclusions generated in the alloy when deoxidation is insufficient Causes surface flaws. However, it has been found that surface defects do not occur when the number ratio of nonmetallic inclusions having a major axis of 30 μm or more among nonmetallic inclusions having a major axis of 3 μm or more is 20% or less. Therefore, among the nonmetallic inclusions having a major axis of 3 μm or more, the number ratio of the nonmetallic inclusions having a major axis of 30 μm or more is desirably 20% or less.

製造方法
本発明にかかるFe−Ni−Cr−Mo合金の製造方法では、上述のようにスラグの組成に特徴を有している。以下、本発明で規定するスラグ組成の根拠を説明する。
Manufacturing Method The manufacturing method of the Fe—Ni—Cr—Mo alloy according to the present invention is characterized by the composition of the slag as described above. Hereinafter, the basis of the slag composition defined in the present invention will be described.

CaO/Al 比:3〜10
合金溶湯を効率よく脱酸、脱硫するため、かつ非金属介在物を制御するためには、スラグのCaO/Al比を制御する必要がある。この比が3未満ではAlの活量が低く、脱酸、脱硫することができなくなり、本発明におけるS濃度、O濃度の範囲に制御することができなくなる。一方、CaO/Al比が10を超えて高くなると、合金溶湯中に還元されるCa濃度が高くなり、CaO濃度に富む非金属介在物を多数生成し、Fe−Ni−Cr−Mo合金板の耐食性を劣化させることに加えて、大型非金属介在物が生成されることから、上限を10とした。このようなCaO/Al比に制御するため、CaO成分として、石灰または蛍石、Al成分として脱酸材であるAlの酸化により生成されるアルミナが使用される。または、Al成分として、アルミナ、またはライムアルミネート原料を添加してもよい。
CaO / Al 2 O 3 ratio: 3 to 10
In order to efficiently deoxidize and desulfurize molten alloy and to control non-metallic inclusions, it is necessary to control the CaO / Al 2 O 3 ratio of the slag. If this ratio is less than 3 , the activity of Al 2 O 3 is low, so that deoxidation and desulfurization cannot be performed, and the S concentration and O concentration ranges in the present invention cannot be controlled. On the other hand, when the CaO / Al 2 O 3 ratio is higher than 10, the Ca concentration reduced in the molten alloy increases, and a large number of non-metallic inclusions rich in CaO concentration are generated. Fe—Ni—Cr—Mo In addition to deteriorating the corrosion resistance of the alloy plate, large non-metallic inclusions are generated, so the upper limit was set to 10. In order to control to such a CaO / Al 2 O 3 ratio, lime or fluorite is used as the CaO component, and alumina generated by oxidation of Al which is a deoxidizing material is used as the Al 2 O 3 component. Alternatively, alumina or lime aluminate raw material may be added as the Al 2 O 3 component.

CaO/SiO 比:5〜20
合金溶湯を効率よく脱酸、脱硫するためには、スラグのCaO/SiO比を制御する必要がある。この比の値が20を超えると相対的にAlの活量が高くなってしまい、MgO・Alスピネルの生成が助長され、請求項に記載の非金属介在物に制御することができなくなる。一方、CaO/SiO比が5未満になると、スラグ中のSiO濃度が高くなり、合金溶湯中に還元されるSi濃度も高くなる。その結果、本発明におけるSi濃度範囲に制御することができなくなり、Fe−Ni−Cr−Mo合金板の耐衝撃性を劣化させることから、下限を3とした。このようなCaO/SiO比に制御するため、CaO成分として、石灰または蛍石、SiO成分として脱酸材であるSiの酸化により生成されるシリカが使用される。あるいは、SiO成分として、珪砂を添加してもよい。
CaO / SiO 2 ratio: 5 to 20
In order to efficiently deoxidize and desulfurize the molten alloy, it is necessary to control the CaO / SiO 2 ratio of the slag. When the value of this ratio exceeds 20, the activity of Al 2 O 3 becomes relatively high, and the formation of MgO · Al 2 O 3 spinel is promoted, and the nonmetallic inclusions according to the claims are controlled. I can't do that. On the other hand, when the CaO / SiO 2 ratio is less than 5, the SiO 2 concentration in the slag increases, and the Si concentration reduced into the molten alloy also increases. As a result, the Si concentration range in the present invention cannot be controlled, and the impact resistance of the Fe—Ni—Cr—Mo alloy plate is deteriorated, so the lower limit was set to 3. In order to control to such a CaO / SiO 2 ratio, lime or fluorite is used as the CaO component, and silica produced by oxidation of Si that is a deoxidizing material is used as the SiO 2 component. Alternatively, silica sand may be added as the SiO 2 component.

MgO:3〜10%
スラグ中のMgOは、溶鋼中に含まれるMg濃度を請求項に記載される濃度範囲に制御するために重要な元素であるとともに、非金属介在物組成を本発明の好ましい組成に制御するためにも必要な元素である。そこで、下限を3%とした。一方、MgO濃度が10%を越えると、MgO・Alスピネルの生成を助長し、MgO・Alスピネルの個数比率を50%以下に制御することが困難となる。そこで、MgO濃度の上限を10%とした。スラグ中のMgOは、AOD精錬、あるいはVOD精錬する際に使用されるドロマイトレンガ、またはマグクロレンガがスラグ中に溶け出すことで、所定の範囲となる。あるいは、所定の成分範囲に制御するため、ドロマイトレンガ、またはマグクロレンガの廃レンガを添加してもよい。
MgO: 3 to 10%
MgO in the slag is an important element for controlling the Mg concentration contained in the molten steel within the concentration range described in the claims, and for controlling the nonmetallic inclusion composition to the preferred composition of the present invention. Is also a necessary element. Therefore, the lower limit was made 3%. On the other hand, if the MgO concentration exceeds 10%, the formation of MgO.Al 2 O 3 spinel is promoted, and it becomes difficult to control the number ratio of MgO · Al 2 O 3 spinel to 50% or less. Therefore, the upper limit of the MgO concentration is set to 10%. MgO in the slag is in a predetermined range by dissolving dolomite bricks or magcro bricks used in AOD refining or VOD refining into the slag. Or in order to control to a predetermined component range, you may add the waste brick of a dolomite brick or a magchrom brick.

次に、実施例を参照して本発明を詳細に説明する。60ton電気炉において、鉄屑、ステンレス屑、フェロニッケル、フェロクロム、純Ni、モリブデンおよび銅線屑を溶解してFe−Ni−Cr−Mo合金を溶製し、その鋼をAOD精錬、VOD精錬あるいはAOD精錬後VOD精錬の3通りのいずれかの処理で脱炭処理後、石灰、蛍石、フェロシリコン合金およびAlを投入して塩基度を調整して、Cr還元、脱酸および脱硫し、最終的に鋼の成分を調整して、表1に示した成分組成を有する合金溶湯を得、次いで、連続鋳造法、あるいは普通造塊法で鋳造することにより当該合金スラブを得た。ここで、表1のNo.1〜8は発明例を、また、No.9〜15は比較例を示したものである。また、表2は製錬方法と鋳造方法の種類を示し、表中「CC」は連続鋳造法、「IC」は普通造塊法を示す。   Next, the present invention will be described in detail with reference to examples. In a 60 ton electric furnace, iron scrap, stainless steel scrap, ferronickel, ferrochrome, pure Ni, molybdenum and copper wire scrap are melted to produce an Fe-Ni-Cr-Mo alloy, and the steel is AOD refined, VOD refined or After decarburization by any of the three processes of AOD refining and VOD refining, lime, fluorite, ferrosilicon alloy and Al are added to adjust the basicity, Cr reduction, deoxidation and desulfurization, and finally The steel components were adjusted to obtain a molten alloy having the component composition shown in Table 1, and then the alloy slab was obtained by continuous casting or normal ingot casting. Here, no. Nos. 1 to 8 are invention examples, and 9 to 15 show comparative examples. Table 2 shows the types of smelting methods and casting methods. In the table, “CC” indicates a continuous casting method and “IC” indicates a normal ingot-making method.

実施例および比較例において以下の評価を行った。
1.シャルピー衝撃試験
スラブを熱間鍛造した鋼塊の鍛伸方向に鉛直な方向を長手とする試料を切り出し、厚さ:5mm、幅:10mm、長さ:55mmの試験片を作製し、室温、2mmVノッチでシャルピー衝撃試験により耐衝撃性を測定した(JIS Z 2242)。
The following evaluation was performed in the examples and comparative examples.
1. Charpy impact test A sample whose length is perpendicular to the forging direction of a steel ingot obtained by hot forging a slab is cut out to produce a test piece having a thickness of 5 mm, a width of 10 mm, and a length of 55 mm, and a room temperature of 2 mmV. Impact resistance was measured by a Charpy impact test with a notch (JIS Z 2242).

2.合金板の製造可否
鋼塊を厚さ6.5mmに熱間圧延した後にコイルに巻き取り、コイルを冷却後、巻き戻したときにコイルが破断したか否かを調べた。
2. Whether or not an alloy plate can be manufactured The steel ingot was hot-rolled to a thickness of 6.5 mm and then wound around the coil. After the coil was cooled, it was examined whether or not the coil was broken.

3.化学成分
Fe−Ni−Cr−Mo合金の化学成分は、蛍光X線分析により測定した。ただし、Cは赤外線吸収法、Oは不活性ガスインパルス融解赤外線吸収法により測定した。
3. Chemical component The chemical component of the Fe-Ni-Cr-Mo alloy was measured by fluorescent X-ray analysis. However, C was measured by an infrared absorption method, and O was measured by an inert gas impulse melting infrared absorption method.

4.非金属介在物
鋳造後のスラブから試料を切り出し、その試料断面に含まれる長径3μm以上からなる非金属介在物を無作為に30点選出し、EDS(エネルギー分散型X線分析)により定量分析し、非金属介在物の同定を行った。
4). Non-metallic inclusions A sample is cut out from the slab after casting, 30 non-metallic inclusions with a major axis of 3 μm or more included in the sample cross section are randomly selected and quantitatively analyzed by EDS (energy dispersive X-ray analysis). The non-metallic inclusions were identified.

また、鋳造後のスラブから試料を切り出し、その試料断面100mmあたりに含まれる長径3μm以上からなる非金属介在物の長径を光学顕微鏡観察により測定し、そのうちの30μm以上の介在物個数比率を得た。 In addition, a sample is cut out from the slab after casting, and the major axis of the nonmetallic inclusions having a major axis of 3 μm or more contained per 100 mm 2 of the sample cross section is measured by optical microscope observation, and the inclusion number ratio of 30 μm or more is obtained. It was.

5.合金板表面欠陥有無
熱間圧延合金板を冷間圧延し、その表面1mあたりに非金属介在物起因のスジ状表面疵発生有無を目視にて観察し判定した。
5. Presence or absence of surface defects
The hot-rolled alloy sheet was cold-rolled, and the presence / absence of streaky surface defects caused by non-metallic inclusions was visually observed per 1 m 2 of the surface.

以上の評価の結果を表3に示す(化学成分を除く)。なお、表1において下線は本発明で規定する成分を逸脱するものを示し、表3において下線は、本発明における好ましい範囲を逸脱する場合を示す。
The results of the above evaluation are shown in Table 3 (excluding chemical components). In Table 1, an underline indicates a component that deviates from the component defined in the present invention, and in Table 3, an underline indicates a case that deviates from a preferable range in the present invention.

本発明例1〜8の試料では、成分が全て本発明の範囲に入っており、熱間圧延後、冷却した後にコイルを巻き戻す際に破断せず合金板の製造は問題なく行うことができた。また、製造した合金板の表面に疵は認められなかった。   In the samples of Invention Examples 1 to 8, all the components are within the scope of the present invention, and the alloy plate can be produced without any problem without being broken when the coil is rewound after hot rolling and cooling. It was. In addition, no wrinkles were observed on the surface of the manufactured alloy plate.

一方、比較例9〜15の試料では、下線で示した成分が本発明の規定する範囲から外れているために、耐衝撃性の悪化による熱間圧延後のコイルを巻き戻す際に合金板が破断するか、表面疵が発生するかのいずれか一方、または両方が発生した。   On the other hand, in the samples of Comparative Examples 9 to 15, since the components indicated by the underline are out of the range defined by the present invention, the alloy plate is used when rewinding the coil after hot rolling due to the deterioration of impact resistance. Either one or both of fracture or surface flaws occurred.

比較例No.9、10、13、14、15の試料では、SiとMnの一方、あるいは両方の濃度が本発明範囲を超えて高いため、σ相を形成し、熱間圧延後の次工程の通板が不可能であった。加えて比較例No.13の試料では、スラグ中のCaO/Al比が本発明の好適な範囲を逸脱し、合金中のAlとCa濃度も本発明の好適な範囲を逸脱した。その結果、非金属介在物中のスピネル比率が50%を超え、30μm以上の介在物個数比率も20%を超えた。 Comparative Example No. In the samples 9, 10, 13, 14, and 15, the concentration of one or both of Si and Mn is higher than the range of the present invention, so a sigma phase is formed, and the next plate after hot rolling is passed through. It was impossible. In addition, Comparative Example No. In 13 samples, the CaO / Al 2 O 3 ratio in the slag deviated from the preferred range of the present invention, and the Al and Ca concentrations in the alloy deviated from the preferred range of the present invention. As a result, the spinel ratio in non-metallic inclusions exceeded 50%, and the inclusion number ratio of 30 μm or more also exceeded 20%.

比較例No.14の試料では、スラグ中のCaO/SiO比、MgO濃度が本発明範囲を逸脱し、合金中のSi濃度とMg濃度も本発明範囲を逸脱した。その結果、非金属介在物中のスピネル比率が50%を超えた。 Comparative Example No. In the 14 samples, the CaO / SiO 2 ratio and MgO concentration in the slag deviated from the scope of the present invention, and the Si concentration and Mg concentration in the alloy also deviated from the scope of the present invention. As a result, the spinel ratio in the nonmetallic inclusion exceeded 50%.

比較例No.15の試料では、スラグ中のCaO/Al比が本発明範囲を逸脱して高く、合金中のCa濃度も本発明範囲を超えて高くなった。その結果、CaOに富む非金属介在物のうちに大型の介在物が、多数見られた。一方、比較例No.12の試料では、スラグ中のCaO/Al比が本発明範囲から外れて低く、合金溶湯は十分に脱酸、脱硫されずにO、S濃度ともに高くなった。その結果、熱間圧延工程で耳割れし、次工程に進捗することができなかった。また、介在物は本発明で規定される介在物組成にはならずに、MnO−Al系酸化物が生成していた。 Comparative Example No. In 15 samples, the CaO / Al 2 O 3 ratio in the slag was high outside the range of the present invention, and the Ca concentration in the alloy was also high beyond the range of the present invention. As a result, many large inclusions were seen among the nonmetallic inclusions rich in CaO. On the other hand, Comparative Example No. In the 12 samples, the CaO / Al 2 O 3 ratio in the slag was low outside the scope of the present invention, and the molten alloy was not sufficiently deoxidized and desulfurized, and both the O and S concentrations were high. As a result, ear cracking occurred in the hot rolling process, and it was not possible to proceed to the next process. In addition, the inclusions did not have the inclusion composition defined in the present invention, and MnO—Al 2 O 3 -based oxide was generated.

比較例No.11の試料では、合金中のAl濃度、スラグ中のCaO/SiO比がいずれも本発明範囲を逸脱しており、結果として非金属介在物のMgO・Alスピネルの個数比率が50%を超え、クラスター化した大型非金属介在物が表面疵をもたらした。 Comparative Example No. In the sample No. 11, the Al concentration in the alloy and the CaO / SiO 2 ratio in the slag both deviated from the scope of the present invention, and as a result, the number ratio of MgO · Al 2 O 3 spinel as nonmetallic inclusions was 50. Large, non-metallic inclusions clustered in excess of% resulted in surface defects.

Fe−Ni−Cr−Mo合金は、ニッケル製錬プラントや海洋構造物等へ適用可能である。
The Fe—Ni—Cr—Mo alloy is applicable to nickel smelting plants, offshore structures, and the like.

Claims (3)

質量%で、C:0.001〜0.015%、Si:0.01〜0.30%、Mn:0.01〜0.50%、P:0.020%以下、S:0.0015%以下、Ni:30.00〜32.00%、Cr:26.00%を超え28.00%以下、Mo:6.00〜7.00%、Cu:1.00%を超え1.40%以下、Al:0.001〜0.10%、N:0.15〜0.25%、B:0.0005〜0.0030%、Ca:0.0001〜0.0020%、Mg:0.0001〜0.0050%、O:0.0001〜0.0050%、残部:Feおよび不可避不純物からなるFe−Ni−Cr−Mo合金。   In mass%, C: 0.001 to 0.015%, Si: 0.01 to 0.30%, Mn: 0.01 to 0.50%, P: 0.020% or less, S: 0.0015 %: Ni: 30.00 to 32.00%, Cr: more than 26.00% and not more than 28.00%, Mo: 6.00 to 7.00%, Cu: more than 1.00%, 1.40% %: Al: 0.001-0.10%, N: 0.15-0.25%, B: 0.0005-0.0030%, Ca: 0.0001-0.0020%, Mg: 0 .0001-0.0050%, O: 0.0001-0.0050%, balance: Fe-Ni-Cr-Mo alloy composed of Fe and inevitable impurities. 非金属介在物としてMgO、MgO・Alスピネル、CaO−Al−MgO系酸化物のいずれか1種または2種以上を含み、長径が3μm以上の非金属介在物のうち、MgO・Alスピネルの個数比率が50%以下で、長径が30μm以上の非金属介在物の個数比率が20%以下であることを特徴とする請求項1に記載のFe−Ni−Cr−Mo合金。 Non-metallic inclusions containing one or more of MgO, MgO.Al 2 O 3 spinel, CaO—Al 2 O 3 —MgO-based oxide as non-metallic inclusions and having a major axis of 3 μm or more, 2. The Fe—Ni—Cr according to claim 1, wherein the number ratio of MgO · Al 2 O 3 spinel is 50% or less and the number ratio of nonmetallic inclusions having a major axis of 30 μm or more is 20% or less. -Mo alloy. 請求項1または2に記載のFe−Ni−Cr−Mo合金の製造方法であって、電気炉に原料を装入し、質量%で、Cr:26.00%を超え28.00%以下、Ni:30.00〜32.00%、Mo:6.00〜7.00%含有するFe−Cr−Ni−Mo合金溶湯を溶製し、次いで、AOD精錬、VOD精錬、およびAOD精錬に続きVOD精錬の3通りのいずれかの処理で脱炭した後に、石灰、蛍石、フェロシリコン合金およびAlを投入し、CaO/Al比:3〜10、CaO/SiO比:5〜20、MgO:3〜10質量%からなるCaO−SiO−MgO−Al−F系スラグを用い、請求項1に記載の成分組成となるように溶鋼成分の調整を行い、その後、該合金溶湯を連続鋳造法または普通造塊法にて鋳造し、スラブを製造することを特徴とするFe−Ni−Cr−Mo合金の製造方法。

It is a manufacturing method of the Fe-Ni-Cr-Mo alloy of Claim 1 or 2, Comprising: Raw material is inserted into an electric furnace, Cr is more than 26.00% and 28.00% or less by mass%. Melting Fe-Cr-Ni-Mo alloy melt containing Ni: 30.00 to 32.00%, Mo: 6.00 to 7.00%, then AOD refining, VOD refining, and AOD refining After decarburization by any of the three processes of VOD refining, lime, fluorite, ferrosilicon alloy and Al are added, and the CaO / Al 2 O 3 ratio: 3 to 10 and the CaO / SiO 2 ratio: 5 to 5 20, MgO: using CaO-SiO 2 -MgO-Al 2 O 3 -F -based slag consisting of 3 to 10 wt%, to adjust the molten steel such that the component composition of claim 1, thereafter, The molten alloy is obtained by continuous casting or ordinary ingot casting. A method for producing an Fe-Ni-Cr-Mo alloy, characterized by casting to produce a slab.

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